Two-stage treatment process of pickling wastewater in the cold-rolling production of stainless steel

Based on the characteristics of pickling wastewater in the cold-rolling production of stainless steel, a new processing route, featuring source sludge reduction, wastewater two-stage treatment, heavy metal-contained sludge and calcium salt sludge separating recovery, was proposed. As shown by the research results, after the two-stage process treatment, the effluent water can steadily reach the emission standards, the sludge yield can be decreased by more than 8% ; within the heavy metal-contained sludge, the recovery rates of Fc,Cr and Ni can either reach or surpass 95% ,and the total content ofF and S can drop to around 3%. Therefore,the sludge in the front part can be used as ferric dust. In the calcium salt sludge ,the recovery rate of F can either reach or surpass 85% ,and the total contents of Fe,Cr and Ni can fall below 0.5%. So the sludge in the rear part can be used as fluorgypsum or fluorite. Meanwhile,the results of the analysis on heavy metals leaching toxicity and morphologic distribution indicate that the two kinds of sectionalized sludge are not classified as hazardous wastes, which have a stable behavior and better utilization values compared with the former mixed- sludge.

Sequential separation of Cu(Ⅱ)/Ni(Ⅱ)/Fe(Ⅱ)from strong-acidic pickling wastewater with a two-stage process based on a bi-pyridine chelating resin

A self-synthesized bi-pyridine chelating resin(PAPY)could separate Cu(Ⅱ)/Ni(Ⅱ)/Fe(Ⅱ)sequentially from strong-acidic pickling wastewater by a two-stage p H-adjusted process,in which Cu(Ⅱ),Ni(Ⅱ),and Fe(Ⅱ)were successively preferred by PAPY.In the first stage(p H 1.0),the separation factor of Cu(Ⅱ)over Ni(Ⅱ)reached 61.43 in Cu(Ⅱ)-Ni(Ⅱ)-Fe(Ⅱ)systems.In the second stage(p H 2.0),the separation factor of Ni(Ⅱ)over Fe(Ⅱ)reached 92.82 in Ni(Ⅱ)-Fe(Ⅱ)systems.Emphasis was placed on the selective separation of Cu(Ⅱ)and Ni(Ⅱ)in the first-stage.The adsorption amounts of Cu(Ⅱ)onto PAPY were 1.2 mmol/g in the first stage,while those of Ni(Ⅱ)and Fe(Ⅱ)were lower than 0.3 mmol/g.Cu(Ⅱ)adsorption was hardly affected by Ni(Ⅱ)with the presence of dense Fe(Ⅱ),but Cu(Ⅱ)inhibited Ni(Ⅱ)adsorption strongly.Part of preloaded Ni(Ⅱ)could be replaced by Cu(Ⅱ)based on the replacement effect.Compared with the absence of Fe(Ⅱ),dense Fe(Ⅱ)could obviously enhance the separation of Cu(Ⅱ)-Ni(Ⅱ).More than 95.0%of Cu(Ⅱ)could be removed in the former 240 BV(BV for bed volume of the adsorbent)in the fixed-bed adsorption column process with the flow rate of 2.5 BV/h.As proved by X-ray photoelectron spectrometry(XPS)and density functional theory(DFT)analyses,Cu(Ⅱ)exerted a much stronger deprotonation and chelation ability toward PAPY than Ni(Ⅱ)and Fe(Ⅱ).Thus,the work shows a great potential in the separation and purification of heavy metal resources from strong-acidic pickling wastewaters.